More and more types of USB data terminal products appear, with the promotion of data rate, the increase of functions and the increment of power consumption, a terminal with a USB interface has higher power supply requirements for the USB interface. According to the requirements of the USB communication protocol, the standard power supply current of the USB interface of the computer is 500 mA, in order to guarantee the security of interface power supply, a limited current circuit is set in all power supply circuits of the terminal products, the object is to protect that an output voltage of the USB power supply interface does not drop below a safe value, and there are basically two current-limiting ways, one is to perform current limiting at an output terminal of a Direct Current (DC)-DC converter, requirements of such current-limiting way for the output current ability of the DC-DC converter are not high, that is, the direct current converter with a low output current ability is appropriate when adopting this way; and the other one is to perform current limiting at an input terminal of the DC-DC converter, such current-limiting way is suitable for the output current ability being very high so that the current output by the converter individually can satisfy the demand of current when a time division multiple access load system bursts in working, and it is required to keep a working voltage of the input terminal of the converter not drop or drop a bit.
When the time division multiple access load system works in a burst mode, the instantaneous high current requires that a large capacitance with a certain capacity must be set in the terminal circuit to perform energy compensation, which makes voltages of a USB interface terminal and a load terminal not drop excessively.
In current-limiting ways of the input terminal of the traditional DC-DC converter, a voltage value of the USB protocol specification is not considered with regard to the selection of current-limiting components.